Incorporation of acetoacetate groups into polymers is of interest due to the unique properties of the acetoacetyl group. Acetoacetylated polymers may be readily crosslinked using a variety of chemistries and may have lower solution viscosity in some cases than the parent polymers. They may have higher affinity for water due to the polarity of the acetoacetyl moiety.
Polymers with affinity for water are also increasingly valuable commercially. Solventborne coatings are rapidly being replaced by waterborne coatings and other new technologies due to the environmental concerns about organic emissions from the manufacture and application of solventborne coatings. In this regard, polymers which require a low amount of solvent to produce a solution with a workable viscosity are also desirable.
There is a need in art of waterborne coatings for novel resins which have desirable properties in many areas, such as water affinity, convenient crosslinking chemistry, good film properties, and good compatibility with other coatings resins.
Water-soluble polymers are also valuable for modifying the rheology of aqueous solutions for other applications. In the food industry, for example, they are used as thickeners; in the oilfield industry, they find use as suspension aids; and in the pharmaceutical industry, they can be used as excipients.
Polymers which may be dispersed in water, but are not soluble in water, are exceptionally valuable in the coatings industry. They enable formulation of coatings which have low application viscosity, but at the same time contain low or no amounts of volatile organic solvents.
Acetoacylated cellulose derivatives are of particular interest for coatings and other industrial applications.
Cellulose is a readily available, naturally occurring polymer. It has been shown that some cellulose esters are biodegradable. Cellulose esters are widely used in coatings, pharmaceutical, and plastics applications, and other cellulose derivatives find wide use in oilfield and food chemical applications.
While cellulose esters containing only acetoacetyl groups may be prepared by addition of diketene or tert-butyl acetoacetate to a solution of cellulose in amide/LiCl solution (where the amide is either 1-methyl-2-pyrrolidinone or N,N-dimethylacetamide), there are no general methods for preparing cellulose esters containing acetoacetyl in addition to an aliphatic or aromatic ester group or groups (cellulose acetoacetate ester, or C(AA)E).
There have been only a few references to cellulose acetoacetate esters in the literature, all dealing with cellulose acetate acetoacetates. In Makromol. Chem, 1953, 10, 261-279, Staudinger and Eicher reported the reaction of cellulose diacetate with diketene in acetic acid, with sodium acetate used as the catalyst. They obtained a product with a degree of substitution ("DS") per anhydroglucose unit ("AGU") of 3.0, as measured by elemental analysis.
Synthesis of CA(AA) or any other C(AA)E by reaction of diketene plus another acylating agent with cellulose itself has not been previously known.
Most of the known cellulose solvents are unsuitable for reactions in which cellulose hydroxyls serve as nucleophiles. The solvent systems recently introduced by C. L. McCormick (U.S. Pat. No. 4,278,790, 1981) and A. F. Turbak, A. El-Kafrawy, F. W. Snyder, Jr., and A. B. Auerbach (U.S. Pat. No. 4,302,252, 1981) are exceptions in that they do permit certain such reactions. McCormick and Turbak et al. have taught that cellulose may be dissolved in solutions of lithium chloride in either N,N-dimethylacetamide or 1-methyl-2-pyrrolidinone. McCormick has further taught (U.S. Pat. No. 4,278,790; Polymer, 1987, 28, 2317-2323) that electrophilic reagents may be added to these cellulose solutions to derivatize cellulose. McCormick has prepared cellulose acetate, methyl cellulose, cellulose carbamate, and other derivatives (but not CAA or C(AA)E) in this way.
U.S. Pat. No. 5,008,385 issued to Diamantoglou discloses the making of particular cellulose derivatives by homogeneous reaction in a mixture of dimethylacetamide and/or N-methylpyrrolidinone with LiCl, preferably after activation of the cellulose starting material in the absence of LiCl. Diketene is mentioned in a long list of components supportive of numerous combinations.
In U.S. Pat. No. 2,521,897, Caldwell describes the reaction of cellulose esters such as cellulose acetate or cellulose acetate butyrate with diketene in a solvent using an amine such as pyridine as a catalyst. The disadvantages of this include the need to esterify cellulose, hydrolyze the resulting cellulose triester, isolate and dry the product and then redissolve and react with diketene. The method also has the disadvantage of the need for use of catalysts in each step, which will be difficult to remove as a catalyst or catalyst salt from a product which has high water affinity.
In U.S. Pat. No. 2,500,029, Hagemeyer describes a process similar to that of Caldwell for the preparation of C(AA)Es. The only improvement introduced by Hagemeyer is that the cellulose ester may be reacted with diketene in a solvent without a catalyst; the reaction is driven thermally. A catalyst is used in the initial esterification of cellulose. The process has all of the other disadvantages of the Caldwell process as described above.
In Das Papier, 42, No. 12, pp. 690-694 (1988), Diamantoglou, et al., teaches esterification of cellulose in solution in DMAC/LiCl or NMP/LiCl with carboxylic anhydrides. He teaches the use of strong acids, amines, and metal acetates as catalysts. In two of the examples shown, no catalyst was used. In these two examples, he observed poor efficiency with respect to the carboxylic anhydride (25-40%) and low product DS/AGU (0.25-1.20). There were no attempts at acetoacetylation nor were any C(AA)Es described.
Clearly, a need exists for a process by which C(AA)Es of the desired degrees of substitution can be prepared directly from solution in order to assure homogeneous substitution along the polymer chains and optimum product solubility. The process must be economical and amenable to scaleup to industrial production. It is desirable to accomplish cellulose acylation without the need for catalysts, so the solvent and lithium chloride could be easily recycled, without interference from salt or catalyst residues. It would also be desirable to obtain materials from this process which would be soluble in water, and other materials, the organic solutions of which would be dispersible in water.